DVD systems have become popular in recent years as home video entertainment systems. DVD systems may also be used to record, store and provide data, such as computer and computing systems, in larger quantities than have heretofore been practicable with other storage devices, e.g., CD-ROM drives.
A conventional DVD system consists of DVD electronics which may be interfaced to a DVD player, a personal computer having a CD-ROM, and a DVD-ROM. Referring to FIG. 1, conventional DVD electronics 10 include photo diodes 11 which receive laser light reflected from a spinning, information-encoded disk and pass the received light to a preamplifier 12 which converts light from an optical signal to an electrical voltage representing the information encoded on the disk. The electrical signals output from the preamplifier are amplified and noise-filtered by channel interface 13, which may be Channel Interface SSI 33P3725 manufactured by Silicon Systems, Inc. of Tustin, Calif. The channel interface 13 includes a built-in phase locked loop (PLL) which generates a data clock that is output, along with the amplified data, to data path controller 14. Channel interface 13 also automatically controls the power of the laser scanning the disk and outputs a signal to a servo digital processor (DSP) 15 which indicates the focus and phase tracking of the laser.
Data path controller 14 decodes, corrects and stores the data received from the channel interface 13 in a DRAM buffer 18 for output, which will be described in detail later. Data path controller 14 generates and outputs a CLV signal to a servo DSP 15. Based on this signal and the focus and tracking signals received from channel interface 13, servo DSP 15 generates and inputs a control signal to motor drivers 16 that control the spindle motors spinning the disk, the movement of the laser read heads, and the focus of the laser (not shown). Servo DSP SSI 33H3825 and Data Path Controller SSI 33C3925 are examples of such devices.
The above-described DVD electronics configuration may be interfaced with a variety of devices including a DVD source decoder (MPEG-2/AC-3 decoder) 20, an ATA packet interface (ATAPI) host 21, and a stereo DAC 17. Microcontroller 19 includes firmware that is programmed to implement the applicable interfaces. Various problems have arisen with prior art interfaces to the DVD Source Decoder.
For example, conventional interfaces have occupied a large number of pins on the data path controller chip ("pins" are terminals by which electrical signals are carried to/from a chip), which is undesirable in view of physical space limitations and increased design complexity. Further, a device interfaced to prior art DVD electronics may not be able to initiate a request for data from memory.
Interfaces in the prior art have also been prone to "lock-up," which causes both the data path controller and the interfaced device to be placed in a wait state simultaneously and indefinitely. Lock-up occurs due to miscommunication during conventional "handshaking" procedures. In the usual scenario, a requesting device sends a request signal in the form of a pulse (a signal which changes from a low level to a high level for a short period of time and returns to the low level) and awaits an acknowledge signal from a source device. If, however, the request pulse is lost during transmission, the source device will never send its acknowledge signal and the requesting device will not know that its request pulse was lost. Even if the source device periodically samples the request signal to check for data requests, the lost pulse would not be detected because the signal on the data request line returned to the low level. The result is that both the requesting and source devices remain stalled, waiting for one another to send a signal.
What is desired is a simple, effective interface utilizing a small number of pins which allows a requesting device to initiate data requests and which avoids the phenomenon of lock-up.